Electrolytic cell for fused baths



Match 30, 1943. R. J. McNlT-r f l :ELECTROLYTIC CELL FOR FUSED BTHSFiled Nov. 18,V 1959V 2 Sheets-Sheet l www, ATTO RN EYS March 30, 1943.R. J. MGNITT,

ELECTROLYTIC CELL OR FUSED BA'I'HSv Filed Nov.v 1a, 1959r 2 sheets-sheet2 e Patented Mar. 30, 1943 UNITED STATES PATENT QF'FlC-EA,

' ELEcrRoLYrrc cau. FOR FUsEn Barns Robert J. McNitt, Perth Amboy, N. J.Appiication November 1s, iaaajseral No. 305,212 1o claims. (o1.2011-247) This invention relates to the electrolysisY of fused bathsandin particular to the production of light metals by the electrolysis offused mixed baths, wherein the compound of the metal sought is fusedwith oneV `or more fiuxing substances to Alower the melting point. ofthe bath. In such electrolytic operationsV to which Vthis inventionpertains, a' cathode stream of electrolyte circulates in the bath,flowing upward into the zone 'of .electrolytic action and downward pasta surface of the cathode which lies4 outside of the zone of electrolyticaction. This invention has for an object the provision of an`improved-method of, and apparatus for, effecting an improvedkcirculation of the cathode stream of electrolyte.-

CII

f lytic cell;

I In the electrolysis of fused mixed baths'v it is important that thereshall ble adequate circulation of the electrolyte to insure that in allparts of the zone of electrolytic action, the various constituents ofthe electrolyte shall always be present in suitable proportions.

In small cells satisfactory circulation of the electrolyte is maintainedby convection currents therein. Heat liberated by the flow of electriccurrent between the electrodes, raises the temperature and lowersthe`density of the electrolyte in the zone of electrolytc action. Inother parts ofthe cell, heat departs from the bath causing a fallintemperature and a rise in density. Due Vto this difference in densitycirculation of the bath occurs, upward at the active cathode surface,and downward in other parts of' the cell.`

This circulation has been found inadequate in I cells having cathodes ofextensive area set close to the anode surface, as is desirable formaximum economy, and it is the aim of my invention to remove thislimitation.

This invention aims to improve the circulation of the cathode stream ofelectrolyteV by repressing the flow of heat from the zone ofelec-Vtrolytic action into the downward streamf of electrolyte therebyincreasing its rapidity of flow. To this end `I repress the-flow of heatby Vmeans of a thermal barrier imposed between the downward stream andthe zone of electro.-

lytic action. Y I y The thermal barrier may consist of one or more solidwalls or partitions together with one or more liquid or gaseous films orbodiessuch, for

example, as a partition having liquid or gaseous of the upward anddownward stream. r`The thertween the bodyof the cathode, and thedownward stream, or it may be in both positions. Y

As an example, I shalldescribe my invention as applied to a cell for theelectrolytic production of sodiumfrom a fused bath consisting of sodiumchloride,with one or more fluxing agents.

The accompanying drawings illustrate more or less 'diagrammaticallyapparatus embodying the invention, in which;

Fig. 1 is a vertical section through an electro- VFig. 2 is a horizontalsection taken at line 2 2 of Fig. 1;

Fig. 3 is a fragmentaryvertical sectional view of a cathode'andv thermalbarrier, and

Figs. 4, 5, 6 7 and 8 are fragmentary vertical sectional views ofmodified Aforms yof thermal barriers.k

As illustrated in thedrawings, the cell I comprises a steel shelloricontaining vessel 3 lined withlla refractory 4. 'A cylindricalgraphite anode 5 having an activey surface A passes up through thebottom of the shell and isconcenf tric therewith. An annular steelcathode 6 Yhaving an active surface B and a .lessactiveer inactivesurface C is mounted raround the anode and supported by two arms 1 whichpass tlir/ough the cell wall and serve to conduct the Vfelectric.current from the cathode to the outside of thev cell. A cylindricalperforated diaphragm 8 is hung concentric with-the active cathode'andanode surfaces and is supported by a steel coillector `9 which is inturn suspended from beams (not shown) which rest on the top of theshell`3. The collector 9 serves to collect anddeliver fr om the cell theproducts of electrolysis, namely,

Vchlorine gas by way of the dome III and duct II and liquid sodium bywayof hood I2 and duct I3. Around the outside of the cathode 6, I place`a thermal barrier comprising a'composite partition I4 having a steel'vessel` I 5, filled :with a films adjacent thereto, or arpartitionforming a passage containing a liquid maintained at tem- `in turn restson the ltop of the cathode' 6;

Y thermal insulating material, such as diatomaceous earth',.and a steelskirt I6 .closed at the top suspended from asteelY angle ring Il, whichThe steel vessel I5 is inserted inside: the skirt -and is therebyenclosed ron` the sides and top.

yVessel I5 is closed at the bottom and on all sides, but is open at thetop, while skirt I6 is closed against entrance of the molten bath at thetop and on all sides, but is open at the `bottom.

In the type of cell shown, I prefer to make the thermal insulating.barrier I4 in two sections suspended from the angle ring I'I which maybe lowered into position aftery the fused bath has been .prepared aroundthe electrodes. Steel wings I8 serve to guide these sections to theirproper positions, and also torclose the spaces between the-ends of thesteel skirts-l6 and the cathode arms'fl. Y

The lcathode stream of electrolyte comprises an upward stream I9 and adownward stream 20. 'Ihe upward stream I9 passes between the factive.,surface B of the cathode and thecliaphragm 8 in what has been referredto herein as the zone of electrolytic action, andthe downward stream 20passes between the barriers I4 and the refractory lining 4. While thereis electrolytic action between the surface A of the anode and thediaphragm, the zone of electro- -lytic action to which reference is madeherein is between the active surface B of the cathode 6 and thediaphragm 8.

'I'he thermal partition I 4 taken alone, will effectively check theflow. the heat from the upward cathode stream of electrolyte I9 in thezone of electrolytic action, through the cathode body and into thedownward stream .20 thusreduclng the counter .currents in the latterand, by permitting a greater difference in temperature and specificgravity between the rising andrfalling streams of electrolyte, result ina more effective circulation of replenished bath past the active cathodesurface. I may, however, providea more enicient thermal barrier byspacing the thermal insulating partition I4 a short distance away fromthe cathode 6, thus forming passages 2| which are connected with thezone of electrolytic action by a lplurality of small openings 22 throughthe cathode. The relatively -cool replenished lelectrolyte enteringthese passages at the bottom 23, becomes lessdense as it absorbs heatthroughthe cathode body 6, and rising in the passage flows throughopenings 22 into the zone of electrolytic action, taking the place ofthe electrolyte which has Ibeen decomposed by the electric current, andrestoring to the electrolyte in the zone of electrolytic action most ofthe heat 'The thermal partition I4 includes a number of gaseous andliquid films which impede the flow of heat. Each of the verticalsurfaces of the steel skirt I6, and the exterior surfaces of the yesselI5 have liquid films of electrolyte in contact therewith, and theinterior vertical surfaces of the vessel I5 have gaseous films incontact therewith. In certain types of cells requiring a verysubstantial repression of the flow of heat, the thermal partition I4 asarranged in Fig. 1 is particularly desirable. In cells requiring alower'repression of the iiow of heat into the downward stream, I maydispense. 'with one or more of the thermal insulating media comprisingthe complete partition I4. For example, I may emlploy vessels I5 in thebarrier, with or Without the diatomaceous earth, and I may use theskirts I6 alone,.omitting the vessels I5 as shown in Fig. 4. f

Under certain operating conditions, the simple and effective thermalbarrier illustrated in Fig. 3 may be used. This thermal barrier consistsof asingle wall or partition of sheet steel 24 spaced from theoutersurface of the cathode 6 forming the passage 2|. wall 24, twoliquid films a'djacent thereto, and the stream of electrolyte in thepassage 2|. In this operation, the rising stream of relatively coolelectrolyte in passage 2 I, together with the liquid films and metal,afford ample repression of the flow of heat from the upward cathodestream I9v mit limited circulation of the stream of cool bath whichescapes therefrom through the body of the r cathode. Moreover, thestreams of cool bath flowing'up through passages 2| maintain a lowertemperature at the surfaces of insulating Aparti-- tion I4 which areadjacent to the cathode than would be possible if the streams were notflowing through passages 2 I.

I prefer to space the openings 22 more closely together in the upperpart of the cathode body and to make the bottom of the openings inclinedat an angle greater than 35 degrees with the horizontal to avoid theaccumulation of sedimentary matter therein.

By means of the combinationof the thermal insulating partition I4 andthe auxiliary stream of electrolyte rising in passage 2I and feedingthrough openings 22 in the cathode into the zone of electrolytic action,I form an effective thermal barrier repressing the flow of heat from therising stream of electrolyte in the zone of electrolyticV action,through the body of the cathode and into in-this passage. But this-method is much less (advantageous than the method 'in which the streamof bath in passage 2| flows through openings 22 in the cathode body. v

There are .advantages in combining the thermal insulating 'partition I4of Fig. 1 with the form of construction illustrated in Fig. 3' to formra thermal barrier of greater effectiveness.

'In other constructions, I may dispense with the passage 2| and theopenings 22 and merely fasten a refractory thermal insulator tothefinactive side C of the cathode as shown in Fig. 5 in which the ironstrap 30 secures the insulation 3| to the cathode. I may also insert.thermal insulation 33 in chambers provided in the body of the cathodeas shown in Fig. 6. On the other hand, a passage 34, answering the samepurpose as passage 2 I, may be provided in the body of the cathode withopenings 35 similar to openings 22 leading to the zone of electrolyticaction, and a thermal insulating partition 36 may be inserted betweenthis passage and the downward stream 20 as shown in Fig. 7, if theconditions should be severe.

The thermal barriers illustrated in the draw ings extend throughout thelength of the 4cathode and in most operations this is the preferred formof barrier. It is understood, however, thatv the barriers need not, forall purposes, extend the full length of the cathode, and the inventionincludes barriers that are relatively short as compared to the cathode.The upper portion ofthe thermal barrier has a pronounced effect upon thetransfer of heatand I may accordingly use relatively short barriers, forexample, a barrier 31 whichis less than half the length ofthe cathode asshown in Fig. 8.

'Ihis barrier includes the metal I claimil l. In/a cell for Ytheelectrolysis of fused 'mixed baths -having a cathodaananode andadiaphragm between the anode`a11d the cathode,the active surfaces of thecathode and the anode being varrangedvin upright positionsproviding anarrow upright space therebetweenpan upright v space along the inactiveside of the; cathode connecting bothl abovel and belov'vftlie cathodewith the narrow upright space, said cell being arranged to be sooperatedthat a vstream of electro-f lyte circulates inal loop'upward intheupright narrow space between the active sidel of the cathode and thediaphragm and downward in the upright space along the inactive side ofthe cathode, the improvement which comprises a thermal barrier includinga partition arranged between the inactive side of the cathode and thedownward stream of electrolyte extending substantially the length of thecathode and so spaced therefrom that a part of the stream of electrolyteflows into the space between the thermal bare rier and the cathode, anda plurality of openings in the cathode through which the stream of elec.trolyte in the space between the thermal barrier and the cathode flowsinto thev upright narrow space between the active surface of thercathodeand the diaphragm. Y

2. A cell for the electrolysis of fused mixed baths which comprises areceptacle for the bath, an upright anode, an upright cathode having aplurality of spaced openings therethrough, an

upright diaphragm spacedV between the active surfaces of the anode andthe cathode, an upright partition extending along the inactive surfaceof the cathoderfrom the top toward` the bottom thereof, an 'uprightspace betweenthe cathode and the partition, a member closingthe space atthe upper parts of the cathode and theA partition, `a passageway throughwhich the hot cathode stream ofA electrolyte flowing upward between thecathode and diaphragm flows over the top of the cathode and partitionand' downward along the partition, and passage means permitting a partof the downward'stream to pass .into the space between the cathode andthe partition and through the openings and another part the topofthemetal plate and the cathode, and

a plurallty'o'f Vholes in the said means permitting the passagetherethrough ofv a stream of electroandthe inactive .surface of thecathode.

5;*A-cell', for the electrolysis of fused lmixed baths which comprisesan upright anode, an up- ,lytejrisin'g in'jthe space betweenthe metalplate right cathode, an upright 4diaphragm' spaced between the activesurfaces ofthe anode and the` cathode, an upright thermal barriermounted near the inactiveside of the cathode proportioned andarranged'to extend over substantially the entire inactive sideof thecathode, an upright walljspaced from the thermalrbarrier forming apassageway between the wall a'nd the thermal barrier for the downwardflow of electolyte, "said thermal barrier comprising'a plurality ofspaced upright metal plates, and a thermal -l insulating medium betweenatleast two of the plates, whereby the flow of heat from the cathodefinto the electrolyte the passageway is suppressed.

6. A cell for the electrolysis of fused mixed baths-which comprises anupright anode, an upright cathode, an lupright diaphragm spaced be-'near the inactive side of the cathode, said thermal barrier comprisinga plurality of spaced upright thereof topass upward between the cathodeand the diaphragm.

3. A cell for the electrolysis of fused mixedbaths which comprises anupright anode, an upright cathode, an upright diaphragm spacedbetweenvthe active surfaces of the anode and the cathode, a plurality ofspaced openings in the cathode, a wall spaced from and extending alongthe inactive surface of the cathode, and an upright thermal barriercomprising a metal plate right passage along the' inactive side of thecathode, and another passage between the thermal barrier and the wall. I

4., A cell for the electrolysis of fused mixed baths which comprises anupright anode, an upright cathode, anupright diaphragm spaced betweenthe active surfaces of the anode and the cathode, an upright wallextending along and spaced fromy the inactive surface ofthe cathodeforming a passageway through which electrolyte flows downward, anupright thermal barrier Ain the Vsaid passageway comprising a metalplateextending from'the top of the cathode towards the bottom and spaced'from the inactive surface of the cathode, 'means closing the spacebetween l of the cathode and Abetween the upward and `spaced between thewall and the inactive surface i of the cathode extending throughout thegreater part of the length of the cathode forming an upmetal plates, aspace between at least two of the plates for confining a gas, andanother thermal insulating medium enclosed between two of the plates,whereby the flow of heat from the cathode into the electrolyte in thepassageway is suppressed.

r7. 1n a'ceu for. the electrolysis of fused baths l having an anode, jacathode and a diaphragm arranged in upright positions and so spaced from.'eacrh other as to form a narrow passageway be- J`tween the diaphragmand the active surface of the cathode and another passageway along theinactive surface of the cathodeand opening means connecting the saidpassageways both above and below the cathode, whereby the same stream ofelectrolyte may VflowV upward in/the narrow passageway and downwardinthe other passageway, the improvement which comprises aV thermalbarrier mounted near the inactive side downward streams which 1sconstructed and arranged to repress the flow of heat from theelectrolyte on thev active side of the cathode through the cathode tothe electrolyte along the inactive side of the cathode.

8. In the electrolytic cell according to claim 7, said thermal vbarrie'rcomprising a plurality of insulating media including solid and fluidmaterials.

9. In a cell for the electrolysis of fused baths having a cathode, ananode and a diaphragm ar-v ranged in 'upright positions and so spacedfrom each other as to form a narrow passageway beween the diaphragmandthe active surface of the cathode and another passageway valong theinactive surface of the cathode and opening means vconnecting the saidpassagewaysy both above and below the cathode. whereby the same streamofelectrolyte may 'now upward in the narrow passageway and downward in theother passageway, the improvement which comprises a lmetal partitionplaced along and spaced from the inactive surface ofthe cathode andbetween the upward and downward streams to provide apassage in whichmolten electrolyte may enter, `said partition and molten electrolyte inthe passage comprising a thermal barrier which represses the flow o fheat through the cathode.

10. In a. cell for the electrolysis of fused salt vbaths having anupright cathode, an upright anode and an upright diaphragm between theanode and the cathode, the active surface of the cathode and thediaphragm being arranged in upright positions providing a narrow uprightspace therebetween, an upright wall laterally spaced fromY the cathodeforming an upright space along the inactive side of the cathode con-A"necting both above and below the cathode with iyte-in the uprightspace along the inactive surface.

'ROBERT J. MCNI'I'I.

